A flat key with a transmitter is known for example from GB 2,273,128 A. The code transmitter is provided together with the ferrite antenna in a recess in the tip of the shaft. Thus, a considerable part of the shaft cannot be provided with locking depressions for the tumblers of the lock.
Further it is known to dispose the code transmitter and the ferrite antenna in a plastic sheath on the broad sides of the bow of a flat key. However this forms a voluminous key which is bulky in a bunch of keys.
German patent application 195 17 728.2/U.S. patent application Ser. No. 08/646,472 discloses a reversible flat key wherein two ferrite antennas are disposed on the two narrow sides of the bow on the side of the bow facing the shaft.